OTTAWA - World leaders descending on the Big Apple this week for the United Nations' annual gabfest can expect the Mideast to take centre stage.

The 68th General Assembly gets underway Monday with global attention focused on Syria's civil war and the red line U.S. President Barack Obama set last year on that regime's use of chemical weapons.

The cast of characters - along with international crises - has shifted since then.

In 2012, Israeli Prime Minister Benjamin Netanyahu memorably set red lines of his own - threatening military action against Iran over its nuclear program.

Now Iran's bellicose former president, Mahmoud Ahmadinejad, who used his appearances on the UN soapbox to rain vitriol on Israel, has been replaced with the softer-toned Hassan Rouhani.

Rouhani is expected to continue the charm offensive at the UN he launched in recent weeks in a bid to relieve Western sanctions against Iran for its nuclear plans.

Prime Minister Stephen Harper has twice addressed the UN General Assembly, in 2006 and 2010, but will shun the spotlight again this year.

Harper will instead spend Wednesday in bilateral meetings with other world leaders and co-hosting a UN event on improving global maternal and child health - an initiative launched by the Conservative government in 2010.

On Thursday, he will take part in a moderated talk on the economy hosted by the Canadian-American Business Council.

Foreign Affairs John Baird will make a repeat appearance before the 193-member council in Harper's stead.

Canada made its disdain for Iran's regime - and its frustration with the UN's lack of action on issues like Syria - clear at the last assembly.

Our diplomats walked out on Ahmadinejad speech while Baird used his to call Iran "the most significant threat to global peace and security."

Baird said on Sunday Canada hasn't yet decided whether its delegates will be in the audience when Rouhani takes the stage.

"It's self-evident the person with the most power, most of the authority, most of the influence (in Iran) is the Supreme Leader (Ali Khamenei). Of course, that position was not open for election," he said.

"We take note of comments President Rouhani has made but what we want to see are actions."

While it's common practice for foreign ministers to speak at the general debate instead of a country's president or prime minister, some view Harper's decision not to speak as a snub.

Under the Conservative government, Canada has had a strained relationship with the UN, though it remains among the body's top donors.